Method and apparatus for particle separation including mechanical separation of particles

ABSTRACT

The present invention relates to a method for separating entrained particles from a gas in a fluidised bed reactor system and fluidised bed reactor system including a particle separator for separating entrained particles from a gas. The particles are separated from the gas flowing in a direction other than the main gas flow direction, whereby the separation is multidimensional. The gas is allowed to pass from the outside of the configuration to the inside thereof and/or vice versa, wherein the particles are separated from the gas during such a travel. The gas flow can be multileveled.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to a method for separating entrainedparticles from a gas in a fluidised bed reactor system and a fluidisedbed reactor system including a particle separator for separatingentrained particles from a gas.

BACKGROUND ART

In the fields of pyrolysis, gasification and combustion, it is common toprovide the reactor of a boiler or a combustion apparatus with a bed ofparticles, which, among other advantages, greatly enhances heat transferbecause of the high heat carrying capacity of the particles. The bed isusually placed in the lower portion of the reactor. Fluidising air orgas entrains the particles with a gas flow inside the reactor. At theupper portion of the reactor, or outside the reactors the particles areseparated from the gas flow by separators. In a circulating fluidisedbed the particles are recirculated to the lower portion of the reactor,from where they can once again be entrained in the gas flow.

There are basically two types of separators: non-centrifugal mechanicalparticle separators and cyclone-type particle separators.

Examples of non-centrifugal mechanical particle separators are disclosedin WO 83/03294, U.S. Pat. No. 5,025,755, U.S. Pat. No. 5,082,477 andU.S. Pat. No. 5,064,621.

In WO 83/03294 a boiler is disclosed having a non-centrifugal mechanicalparticle separator outside the reactor.

In U.S. Pat. No. 5,025,755 an apparatus is disclosed having anon-centrifugal mechanical particle separator in the upper portion ofthe reactor.

An example of a cyclone-type particle separator disposed in the upperportion of a reactor is disclosed in U.S. Pat. No. 5,070,822.

SUMMARY OF THE INVENTION

An object of the present invention is to achieve a compact particleseparator.

Another object of the invention is to achieve a particle separator thatis easily mountable and demountable inside a reactor.

These and other objects which will become apparent in the following areachieved by a fluidised bed reactor system and a method for separatingparticles as defined in the accompanied claims.

The present invention is based on the insight of the advantages ofseparating particles in a direction other than the “main flowdirection”. The term “main flow direction” is generally referred to hereas the direction of a line drawn between a point before the gas entersthe separator and a point after the gas exits the separator. In priorart non-centrifugal mechanical separators, the separator elements areconventionally positioned so as to separate the particles from the gasflowing substantially in the “main flow direction”. In other words, theseparation direction is one-dimensional. According to the presentinvention, however, the particles can be separated from the gas flowingin a direction other than the “main flow direction”, whereby theseparation is multidimensional.

Also, it has been realised that the particle separator can be madecompact in a configuration that allows the gas to pass from the outsideof the configuration to the inside thereof and/or vice versa, whereinthe particles are separated from the gas during such a travel.

According to one aspect of the present invention a method is providedfor separating entrained particles from a gas in a fluidised bed reactorsystem which comprises a separation region defined by a cylindricalr-,φ-,z-coordinate system, the method comprising the consecutive stepsof:

leading the gas in the z-direction (axial direction),

diverting the gas to flow substantially in the r-direction (radialdirection), while keeping the gas circumferentially distributed inrφ-planes, and

mechanically separating the particles from the gas while the gas isflowing substantially in the r-direction.

According to another aspect the present invention provides a fluidisedbed reactor system including a particle separator for separatingentrained particles from a gas having a flow path. The particleseparator comprises a set of non-centrifugal mechanical separatorelements disposed in the flow path of the gas, so that the gas is ableto pass between the separator elements while the inertia of theparticles directs them to the separator elements upon which they impingeand are separated and removed from the gas flow. The set of separatorelements is arranged in a configuration having a centre zone with acentre axis, and a circumference. Directional means are provided fordirecting the gas so that gas passing through the set of separatorelements flows from the circumference to the centre zone of theconfiguration and/or vice versa.

Thus, as mentioned above, according to the present invention theparticles are separated from the gas multidimensionally instead of thetraditional one-dimensional separator passage as far as non-centrifugalmechanical particle separator elements are concerned. In mathematicalterms, instead of a separation in the x-direction in an orthonormalx-,y-,z-coordinate system, the present invention provides separation inthe r-direction in a cylindrical r-,φ-,z-coordinate system, where:

 r=x·cos φ+y·sin φ

Hence, the region where the separation is performed is convenientlydefined by a cylindrical coordinate system. Gas will be led to flow inthe z-direction or axial direction of the separation region. Thereafter,the gas is diverted to flow substantially in the re-direction or radialdirection of the separation region. This does not necessarily mean thatthe gas will be diverted in a direction which is totally perpendicularto the axial direction, but merely that the gas will flow to or from acentre zone. During this diverting action the gas is keptcircumferentially distributed in rφ-planes, i.e. disk shaped planes.Accordingly, the gas does not have to flow from or to just one side ofthe separation region, but substantially from or to the wholecircumference of the separation region. It is during this radial flowthat the particles are separated from the gas.

According to a further aspect the separator elements are arranged as astructure having consecutive particle separation levels X_(N) (X₁,X₂,X₃,. . . , X_(n) . . . ), N being an integer. The directional means arearranged at the circumference and at the centre zone of theconfiguration, so as to cause the gas to flow through the separatorelements in one direction on levels with odd-numbered N and in thereversed direction on levels with even-numbered N.

The obvious advantage of this is that, when the separator elementspreferably being provided as one set of separator elements, one and thesame separator element is passed by the flowing gas repeated times. Thusparticles that have not impinged upon the separator at the first pass,can be captured on the following pass(es), thus making the most of eachseparator element.

Aptly, the configuration has a generally cylindrical shape, preferablywith the separator elements being arranged essentially symmetrically.Note that the term “cylindrical” does not necessarily imply that thecross-section is circular.

Preferably, the separator elements have an elongated shape and extendessentially in parallel with the centre axis.

It is advantageous to use channel-shaped beams as separator elements,the beams having an essentially U-shaped cross-section. The beams arearranged so that the particles impinge upon the bottom of the U and thenfall down, guided by the channel-shaped beam, to be collected.

In order to further enhance the efficiency of the system, the set ofseparator elements can form a number of ring-shaped arrays being placedwithin each other. The separator elements of an array are preferablycircumferentially displaced with respect to the separator elements of anadjacent array.

Consequently, the separator elements of the different arrays can bearranged in a staggered way with an angular offset with respect to eachother. Those particles that do not impinge on separator elements of onearray can be disentrained from the gas to a great extent by theseparator elements of an adjacent array. Of course the number of arraysis chosen according to what is considered appropriate, with respect tocompactness, efficiency etc.

According to a specific embodiment, each separator element, being inform of a U-shaped beam, is provided with a respective additionalU-shaped beam attached in parallel thereto. Moreover, each of theadditional U-shaped beams is provided with a respective further U-shapedbeam attached in parallel thereto, forming a unit with three U-shapedbeam channels. Dividing plates are inserted in at least two U-shapedbeam channels for mechanical segregation of said channels and a sectionof at least one of the elements in the unit is removed, so as to createthree particle separation levels of impinge areas, one for each elementin the unit. Directional means are arranged to direct the gas inalternating level directions.

A three-channel unit design can be constructed with three identicalU-beams or with three non-identical U-beams. For instance, a tapereddesign may be used. This is particularly practical inside a circularreactor shaft, in which case the element located nearest the shaftcentre would have a smaller cross-section than the intermediate element,which in turn would have a smaller cross-section than the elementfurthest away from the centre.

Due to the configuration of a particle separator according to theinvention, it is particularly suitable for disposal inside a reactorshaft. Even though the separator elements are preferably arranged in asymmetrical and circular configuration, it is also possible to arrangethe separator elements in other configurations, such as triangular,square, other polygon or in any other desired way. When the particleseparator is intended to be used inside a reactor shaft, it isfavourable to have the configuration adapted to the cross-section of thereactor shaft.

After the particles have been disentrained they fall down from theseparator elements to some form of collector located below. Thedisentrained particles can advantageously be recycled to the reactor bedby a standpipe.

When the particle separator is disposed inside the reactor, an internalstandpipe located around the centre axis of the reactor can be used. Inthis case, the fluidising gas with entrained particles suitably flowsfrom the bottom portion to the top portion of the reactor, generallysymmetrically around the internal standpipe. The particle separator,preferably being disposed at the top portion of the reactor, disentrainsthe particles from the gas, which exits the reactor. The particles arethen recycled through the internal standpipe in the centre of thereactor.

Of course it is also possible to let an internal standpipe be positionedoff-centred, e.g. extending along the wall of the reactor. In this caseit might be desirable to have more than one standpipe. The choice of anoff-centred alternative provides for the possibility of letting the gasenter the particle separator from the centre of the configuration andconsequently the disentrained particle can advantageously be caused tofall down at the circumference thereof.

The above description is related to a circulating fluidised bed. Theperson skilled in the art will realise that the present invention can beutilised in other connections as well. The skilled person will alsorealise that the particle separator of the present system can be locatedoutside a reactor, and not only inside.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be more closely described in the following inrelation to non-limiting embodiments thereof with reference to thedrawings, in which:

FIG. 1 illustrates schematically a cross-section of a fluidised bedreactor system according to the present invention.

FIG. 2 illustrates an example of a cross-section through the particleseparator in the top portion of the reactor in FIG. 1.

FIGS. 3a-3 b illustrate different particle separator arrangements.

FIGS. 4a-4 c illustrate different types of separator element unitsconsisting of three integrated U-shaped beams.

FIGS. 5a-5 c illustrate the three U-shaped beams of FIG. 4cindividually.

FIG. 6 illustrates the flow path through the beams of FIGS. 5a-5 c, whenthey have been attached to each other.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

FIG. 1 illustrates schematically a cross-section of a circulatingfluidised bed reactor system 1, comprising a particle separator 4,according to the present invention. The system 1 has an elongatedreactor 6, in which a particle bed is disposed in the lower portion ofthe reactor 6 on a distributor plate 8. Below the bed is an inlet 10 forprimary gas, and above are two inlets 12 for secondary gas. The reactor6 has an enlarged cylindrical top portion, the outer wall 13 of whichhas a larger diameter than the rest of the reactor 6. A particleseparator 4 having elongated U-shaped beams 14 as separator elements,constituting a cylindrical configuration, is housed in said top portion.In use, the flow path of the gas is as follows. Primary gas enters thereactor 6 through the inlet 10 for primary gas, is distributed bydistributor plate B, entrains particles from the particle bed, travelsvertically up the reactor 6, mixes with secondary gas entering from theinlets 12 for secondary gas, reaches the particle separator 4 where theonly path available for the gas is horizontally through the particleseparator 4, thus passes the U-shaped beams 14 and finally exitsvertically through a gas outlet 16.

However, the majority of the particles entrained in the gas flow areseparated therefrom by-the elongated U-shaped beams 14. The particlesfall into a funnel-shaped particle collector 18 and are returned to thebottom portion of the reactor 6 through an internal standpipe 20, sothat they can be entrained in the gas flow again. The standpipe 20extends in the centre of the reactor 6 from the bottom of the particlecollector 18 to a level between the inlets 12 for secondary gas and thedistributor plate 8.

The gas and any particles by-passing the U-shaped beams 14 then pass toa conventional cyclone 100. Material disentrained by the cyclone 100fall into an external standpipe 102 and are recycled through a line 104running from a port 106 just above the base of the external standpipe102 to a port 108 on the reactor 6 between the distributor plate 8 andthe inlets 12 for secondary gas. Recirculation is initiated byfluidisation of the external standpipe 102 via a distributor plate 110at the base. Gas from the cyclone 100 passes to an exhaust stack 112.

FIG. 2 illustrates an example of a cross-section through the particleseparator 4 in the top portion of the reactor 6 in FIG. 1. As can beseen, two rings 22, 24 of U-shaped beams 14 are arranged concentrically,within the outer wall 13 of the top portion. The small arrows indicatethe direction of the gas as it enters the configuration. Even though thefigure illustrates a radial gas flow from the outside to the inside ofthe configuration, the skilled person appreciates that the reversedirection would also be practicable, in which case the U-shaped beams 14would suitably be turned around with the opening of the U facinginwards. In the figure the beams of the inner ring 24 are displaced inthe circumferential direction of the reactor with respect to the beamsof the outer ring 22. With this arrangement the beams of the inner ring24 effectively shield the gas that by-passes the beams of the outer ring22.

FIG. 3a illustrates a configuration having a stacked multileveled gasflow. The top of each beam 14 is mounted to a suspension attachment 15so that the beams 14 are vertically suspended. The beams 14 can befreely suspended so as to allow them to expand in their longitudinaldirection as the temperature rises. The illustrated configuration ofbeams can be said to comprise three main levels or sections; a lowersection A, a middle section B and an upper section C. The beams 14 aresupported by horizontal support plates 26 a-c (three shown) connected bysupport bars (not shown) to hold the support plates 26 a-c in correctvertical alignment. The support plates 26 a-c define the top of eachsection A-C. A cover plate 28 disposed in the centre of theconfiguration is mounted on top of the middle support plate 26 b. Thesupport plates 26 a-c and the cover plate 28 forces the gas to flow inalternating level directions, as indicated by the solid arrows in thefigure. Thus, when the gas vertically enters the configuration at thelower section A, the support plate 26A redirects it into the horizontaldirection to a radial inwardly flow. Next the gas passes up to themiddle section B, where it is forced by the cover plate 28 to once againflow horizontally, this time in a radial outwardly flow. Thereafter,having reached the upper section C, the gas is forced to flow inwardlyby the support plate 26 c. Finally, the gas vertically exits theconfiguration form the centre thereof. Naturally, support plate 26 ccould be removed without substantially altering the flow path of thegas. Furthermore, although not shown in the figure, the support platepositioning can be made variable and, thus, so can the beam height,making it possible to utilise a larger or smaller part of the beamsaccording to preference. The non-solid arrows represent particlesseparated from the gas flow falling from the bottom of the U in thebeams into the funnel-shaped collector 18 and then passing to theinternal standpipe 20. Thus, the particles will impinge on the insidebottom of the U in the beams at sections A and C, if the beams areoriented as in FIG. 2. Of course it would also be possible to turn themin the reverse orientation, or to arrange the beam rings with differentorientations, one beam ring with the opening of the U facing the centreand the other beam ring with the opening of the U facing thecircumference.

In FIG. 3b the cover plate 28 in FIG. 3a has been removed and a pipe 34has been inserted extending from the lower support plate 26 a to the gasoutlet 16. Thus, the gas flows past the U-shaped beams 14 only once.This arrangement gives a shorter residence time through the particleseparator, which at times might be preferred. Depending on stabilityrequirements, the alternative would be to remove the support plates 26a-c in order to take advantage of the full length of the beams 14, asshown in FIG. 1, or only to change the positioning of the support plate26 a-c in order to obtain a desired length.

FIGS. 4a-4 c illustrate different types of separator element unitsconsisting of three integrated U-shaped beams. Similarly to theembodiment shown in FIG. 3a, these triple-units are adapted to providefor a multileveled flow. However, to make this possible a section of oneof the beams must be removed and separating plates be inserted, as willbe explained in connection with FIGS. 5a-5 c and FIG. 6.

Three different constructions are shown in FIGS. 4a-4 c. As has beendiscussed above a tapered construction (FIG. 4a) may be desired, e.g.inside a circular reactor shaft, in which case the beam 40 locatednearest the shaft centre has a smaller cross-section than theintermediate beam 42, which in turn has a smaller cross-section than thebeam 44 furthest away from the centre.

If a tapered design is not considered necessary, the constructionsillustrated in FIGS. 4b and 4 c may be used. The construction of FIG. 4crequires the lowest number of separating plates, and this is theembodiment shown in FIGS. 5a-5 c and FIG. 6. Note that in reality thethree beams 50, 52 and 54 are attached to each other, e.g. by spotwelding, however, in FIG. 4c they are shown somewhat separated for sakeof clarity.

FIGS. 5a-5 c illustrate the three U-shaped beams of FIG. 4cindividually. The beams each have a lower section A, a middle section Band an upper section C, from which three particle separation levels willbe achieved.

In FIG. 5a the first beam 50 is illustrated. At the upper section 50C ofthe beam 50, the bottom of the U has been removed. At the middle section50B of the beam 50 two separating plates 60, 62 are insertedperpendicularly to the bottom of the U, and a plate 64 parallel theretocovering the area between the perpendicularly inserted separating plates60, 62. Thus, a box has been provided over the middle section 50Bmechanically separating the three sections 50A-C from each other.

In FIG. 5b the second beam 52 is illustrated. As can be seen it is astandard U-shaped beam with no modifications.

In FIG. 5c the third beam 54 is illustrated. A separating plate 66 isinserted perpendicularly to the bottom of the U, at the transitionbetween the upper section 54C and the middle section 54B of the beam 54.A plate 68 extending upwards from the separating plate 66 covers theupper section 54C of the beam 54. Thus the upper section 54C ismechanically separated from the middle section 54B and the lower section54A. A plate 70 arranged parallel to the bottom of the U is covering thelower section 54A of the beam 54.

FIG. 6 illustrates the gas flow path (solid arrows) through the beams50, 52, 54 of FIGS. 5a-5 c, when they have been attached to each other,and the respective parts have been depicted with the same referencenumerals. The gas directed by a support plate 72 and separating plate 62enters the configuration at the lower section 50A of the first beam 50.While the particles can impinge on the bottom of the U of the first beam50, the gas passes all three beams (between two adjacent triple-units).Next, the gas flows upwards but is hindered by a cover plate 74, whichcorresponds to the cover plate 28 in FIG. 3a, forcing in co-operationwith separating plate 66 the gas to flow back past the three beams.However, remaining particles can impinge on the bottom of the U of thethird beam 54, at the middle section 54B thereof. Note that the gas canonly enter the third beam 54 at its middle section 54B because of theplate 70 covering the lower section. Thereafter, the gas is caused todouble-back again by a support plate 76, and enters the first beam 50 atthe upper section 50 c thereof. The plate 64 refuses entrance of the gasat the middle section of the first beam 50. Since the bottom of the U isremoved at section 50 c and the separating plate 60 is provided formechanical isolation of the upper section from the other sections, thegas will pass through the first beam 50 to the second beam 52. This timeremaining particles can impinge on the bottom of the U of the secondbeam 52, at the upper section 52C thereof. Finally, having no other wayto flow (because of plate 68 and cover plate 74) the gas exits throughthe gas outlet 16.

This triple-unit beam design is preferably arranged in a circularconfiguration as the beams in FIG. 2. Thus, although not shown, to theleft of the triple-unit is the outer wall of the top portion of thereactor, and to the right is the centre of the reactor (compare with theleft half of FIG. 3).

It is to be noted that numerous modifications and variations can be madewithout departing from the scope of the present invention defined in theaccompanied claims.

What is claimed is:
 1. Method for separating entrained particles from agas in a fluidised bed reactor system which comprises a separationregion defined by a cylindrical r-, φ-, z-coordinate system, the methodcomprising the consecutive steps of: leading the gas in the z-direction(axial direction), diverting the gas to flow substantially in ther-direction (radial direction), while keeping the gas circumferentiallydistributed in r φ-planes, wherein the gas flows to and/or fromsubstantially the whole circumference of the separation region in therφ- planes, and mechanically separating the particles from the gas whilethe gas is flowing substantially in the r-direction, the gas continuingto flow substantially in the r-direction after mechanical separation. 2.Method according to claim 1, comprising the further steps of: causingthe gas having flown in the r-direction to flow in a reversedr-direction, and mechanically separating the particles from the gaswhile the gas is flowing in a reversed r-direction.
 3. Method accordingto claim 1, wherein in the cylindrical coordinate system (r,φ),z) thegas is initially directed from a larger r-value towards a smallerr-value for a first separation step of at least one separation step, andafter a last separation step of the at least one separation step,wherein, in the last separation step the gas is directed towards asmaller r-value, leading the gas away in the z-direction.
 4. Methodaccording to claim 2, wherein in the cylindrical coordinate system(r,φ,z) the gas is initially directed from a larger r-value towards asmaller r-value, for a first separation step of at least one separationstep, and after a last separation step of the at least one separationstep in which last separation step the gas is directed towards a smallerr-value, leading the gas away in the z-direction.
 5. Method forseparating entrained particles from a gas in a fluidised bed reactorsystem, comprising the steps of: causing the gas to flow in a stackedmultileveled flow with consecutive particle separation levels X_(N) (X₁,X₂, X₃, . . . , X_(N) . . . ), N being an integer, directing the gas toflow in a first direction on the first level X₁, bringing the gas to thenext level X₂ from the first level X₁, directing the gas to flow in adirection reversed to the first direction on the next level X₂, so as tocreate a doubled-back flow path, bringing the gas to additional particleseparation levels, so as to cause the gas to flow in the first directionon levels with odd-numbered N and in the reversed direction on levelswith even-numbered N, and mechanically separating the particles from thegas on each level.
 6. Method according to claim 5, in which the gas iscaused to flow from a center zone to a circumference of the center zoneor vice versa, whereby the directions are essentially radial directionsin respect of the center zone and the circumference associated thereto.7. Fluidised bed reactor system including a particle separator forseparating entrained particles from a gas having a flow path, comprisinga set of non-centrifugal mechanical separator elements disposed in theflow path of the gas, so that the gas is able to pass between theseparator elements while the inertia of the particles directs them tothe separator elements upon which they impinge and are separated andremoved from the gas flow, wherein the set of separator elements isarranged in a configuration having a center zone with a center axis, anda circumference, wherein directional means are provided for directingthe gas so that gas passing through the set of separator elements flowsfrom the circumference to the center zone of the configuration or viceversa.
 8. System according to claim 7, in which the set of separatorelements is arranged as a structure having consecutive particleseparation levels X_(N) (X₁, X₂, X₃, . . . , X_(n) . . . ), N being aninteger, wherein the directional means are arranged at the circumferenceand at the center zone of the configuration, so as to cause the gas toflow through the set of separator elements in one direction on levelswith odd-numbered N and in the reversed direction on levels witheven-numbered N.
 9. System according to claim 7, wherein theconfiguration has a generally cylindrical shape, wherein the separatorelements are arranged essentially symmetrically.
 10. System according toclaim 7, wherein the separator elements have an elongated shape andextend essentially in parallel with the center axis.
 11. Systemaccording to claim 7, wherein the separator elements are channel-shapedbeams having an essentially U-shaped cross-section, wherein the beamsare arranged so that the particles impinge upon the bottom of the U andthen fall down, guided by the channel-shaped beam, to be collected. 12.System according to claim 7, in which the set of separator elementsforms a number of ring-shaped arrays being placed within each other. 13.System according to claim 12, in which the separator elements of anarray are circumferentially displaced with respect to the separatorelements of an adjacent array.
 14. System according to claim 11, inwhich each U-shaped beam is provided with a respective additionalU-shaped beam attached in parallel thereto, each of the additionalU-shaped beams being provided with a respective further U-shaped beamseparator element attached in parallel thereto, forming a unit withthree U-shaped beam channels, dividing plates being inserted in at leasttwo U-shaped beam channels for mechanical segregation of the channelsand a section of at least one of the elements in the unit being removed,so as to create three particle separation levels of impinge areas, onefor each element in the unit, wherein the directional means are arrangedto direct the gas in alternative level directions.
 15. System accordingto claim 7, wherein the particle separator is located inside a reactor,and wherein the center axis is in parallel with the axis of the reactor.16. System according to claim 7, wherein the configuration is circularcylindrical.
 17. System according to claim 8, wherein the configurationhas a generally cylindrical shape, wherein the separator elements arearranged essentially symmetrically.
 18. Fluidised bed reactor systemincluding a particle separator for separating entrained particles from agas having a flow path, comprising a set of non-centrifugal mechanicalseparator elements disposed in the flow path of the gas, so that the gasis able to pass between the separator elements while the inertia of theparticles directs them to the separator elements upon which they impingeand are separated and removed from the gas flow, wherein the set ofseparator elements is arranged as a structure having consecutiveparticle separation levels X_(N) (X₁, X₂, X₃, . . . , X_(n) . . . ), Nbeing an integer, wherein directional means are arranged to cause thegas to flow through the various levels of the structure in one directionon levels with odd-numbered N and in the reversed direction on levelswith even-numbered N.
 19. System according to claim 18, in which the setof separator elements is arranged in a configuration having a centerzone with a center axis, and a circumference, wherein the directionalmeans are located at the circumference and at the center zone of theconfiguration, so as to cause the gas to pass through the set ofseparator elements from the circumference to the center zone of theconfiguration or vice versa.
 20. System according to claim 19, whereinthe configuration has a generally cylindrical shape, preferably with theseparator elements being arranged essentially symmetrically.